Existing night vision goggle systems are typically heavy, cumbersome and unstable. They do not even resemble common goggles; but, rather, resemble television cameras mounted on the user's head. Such goggles typically protrude more than 175 mm from the user's eyes and weight as much as 850 grams, and the weight and front-to-back length of such systems exert large moments on the user's head, causing serious instability problems and preventing their effective use in applications in which the user's head is subjected to high gravitational or centrifugal loads.
Night vision goggle systems typically include an objective lens set, an image intensifier and an eyepiece lens set, all arranged in a straight line. The lens design frequently results in an inverted image at the user's eyes. Correction of this condition by the addition of an inverting lens set would only add to the already excessive length of the system and further aggravate the instability problem. Accordingly, the inverted image condition is often corrected by the use of twisted fiber optics in the image intensifier. Twisted fiber optics, however, can also increase the length of the optical system, and can cause distortion in the image presented to the user.
Many existing night vision goggles also cannot handle sudden excessive lighting conditions such as flares or other bright lights. In such conditions, the goggles become inoperative and the image intensifier must be turned off. When the image intensifier is turned off, however, most prior systems become opaque, rendering the user essentially blind.
It is known to provide night vision goggles wherein the main optical assembly is coupled to the user's eye through a periscope-type arrangement, the reflection to the user's eye being provided by a beam splitting prism which is transparent when the system is turned off, permitting the user to look past the main optical assembly. Such arrangements, however, still suffer from many of the disadvantages discussed herein.
Furthermore, prior night vision goggle systems generally have an extremely limited field of view and provide little or no peripheral vision. This renders such systems essentially useless in applications which require peripheral vision, for example, in applications in which the user is operating an automobile, aircraft or other vehicle, and must be able to view an instrument panel or the like without significant head movement.
An improved night vision goggle system which overcomes many of the above limitations of prior night vision goggles is disclosed in U.S. Pat. No. 4,653,879 issued on Mar. 31, 1987. The goggles disclosed in this patent are compact, light in weight, provide the user with both an intensified image and an unintensified or direct image, and are operable in sudden excessive lighting conditions. The resulting goggles can also be effectively used by pilots of high performance aircraft and in other applications where the user's head is likely to be subjected to high gravitational forces or similar loads without causing the instability problems discussed above.
It would be desirable to provide an improved night vision goggle apparatus which incorporates the advantageous features of the goggles described in U.S. Pat. No. 4,653,879; and which, in addition, is of even greater compactness so as to permit the user to also wear an oxygen mask, helmet and/or other conventional equipment, as is often required by pilots of high performance aircraft and others, without interference from the goggles.
It would also be desirable to provide night vision goggles which are capable of providing indicia or other types of secondary images to the user without interfering with the normal use of the goggles. In this regard, modern avionics suites in high performance aircraft typically include numerous information presentation devices to apprise the pilot of aircraft performance and attitude, and to provide other information such as topographical, enhanced scene, or radar data. A modern avionics suite may include, for example, forward looking infrared (FLIR) imaging devices, stabilized telephoto and low-light television imaging devices and radar for imaging and/or thread identification and tracking. A pilot may rely upon the data displayed by one or more of these devices during operation of the aircraft. Similarly, heads up displays (HUDs) of attitude, performance and navigation information are common. Receiving or monitoring such data or information may be vital to the pilot during operation of the aircraft, and it is desirable that the pilot to be able to easily view such secondary indicia or images without having to remove the goggles and in a manner that won't interfere with normal use of the goggles.
It would also be desirable to provide night vision goggles which afford the user with a large field of view; and, in particular, with a peripheral field of view which approaches that enjoyed by persons not wearing goggles.